I haven't noticed a huge difference in Spark vs when they rolled from their original 4g to LTE, but I'm super happy with the 6+ I just got on lease. I like the hell out of the idea for smartphones. It's difficult for me to last the normal 24 month period normally, so having a 12 month option where I'd pay less overall than I would and then I can get the new cutting edge is cool. Logically, this feels short sighted and silly, but /shurg
And typically, I'm not one to be all snobby about feel refinement and ****, but I really like the feel of the 6+ over the note 3 I had prior. It's got a more robust/substantial feel that pleases me. Again, logically, I know it shouldn't matter, but it does /shurg.